The use of high frequency alternating electric current for the melting of certain metals is a well established procedure and one of these furnaces is the coreless type that has a water cooled copper tube coiled around the outside of a crucible that carries the alternating electric current, the metal to be melted being supported in the crucible that is centered within the coil. The high frequency current flowing in the cooled coil induces a current in the metal in the crucible that renders the metal molten.
Another form of an induction furnace for melting metal is a furnace that makes use of an upper case situated above an inductor that encloses a metal core with a coil positioned in the center of the core. The core stands in a vertical position and an elongated current carrying coil is centered in a horizontal position within the core. The core and its coil are embedded in a rammed granular refractory receptacle at the bottom of the furnace and a flow of an alternating electric current is induced in the core when the coil is energized that causes the core to become heated to a degree that is sufficient to melt the metal. When the furnace is in operation molten metal flows through the channel and is heated by its resistance to the flow of the induced current. The hot molten metal is collected in the upper case from which the molten metal is subsequently removed from the furnace.
When solid metal to be melted is fed into the upper case most of the heat induced in the molten metal in the core flows upwardly with the molten metal that is highly heated in the inductor, so that the solid metal is melted and the process becomes continuous, as liquid metal is poured out of the upper case's spout. The refractory receptacle itself that is carried in the inductor, which receptacle supports the channel in which the molten metal is subjected to the induced electrical current flow obviously becomes highly heated as the induction heating of the molten metal in the channel continues. In this type of melting operation it is not practical to provide any cooling means for the core and coil and thus the core or the channel in which the induced electrical current is converted to heat tends to act like a heater in the center of the receptacle.
The typical refractory receptacle used in the core and coil type of furnace is composed of refractory grains that are rammed and packed into place to form a somewhat porous receptacle that surrounds these elements to hold them in their proper relative insulated and spaced apart positions. When the coil which simulates the primary coil of an electric transformer is energized, it causes a high frequency current to flow in the metal in the core or channel which acts like the core of the transformer and a solid or molten metal in the core is heated by the alternating current flow induced therein. In this manner when the furnace is to be started up, the metal in the channel or loop of the furnace is initially heated to its melting point by the high frequency alternating current supplied to the unit and as above explained during the continued operation of the furnace the induced electrical current flow in the molten metal in the channel produces the heat that flows upwardly into the upper case with the highly heated molten stream to melt the solid metal subsequently fed into the upper case.
The core or loop of this type of furnace, is conventionally formed by molding a metal loop to shape and placing it in its solid form in a vertical position in the receptacle for the inductor with the coil disposed horizontally within the center of the loop as the refractory used for supporting the loop and coil is being rammed into place around the solid metal core and its horizontally disposed coil. When one or more of such loops and their coils have been placed in their respective positions and have been built into the rammed refractory receptacle, the furnace is fired up and as the temperature and heat build up in the core means, the solid metal melts and the molten metal then subsequently flows from the channel that has thus been formed in the receptacle by ramming the refractory grains solidly around the molded metal loop to complete the assembly. When the receptacle is being built, the loop means are held in a vertical plane and as the feeding of solid metal into the upper case proceeds and the melting process continues, the molten metal flows continuously from the channel or multiple channels left in the receptacle to carry the heat generated in the loop into the upper case. Since one or more of these loop elements may be built into the core and coil furnace and as the melting process continues more or less indefinitely it is apparent that a considerable quantity of heat is released into the refractory receptacle supporting the loop and coil and in the conventional furnace used today inevitably some molten metal leaks from the channel means to escape into the pores of the rammed refractory receptacle. This molten metal that passes into the pores of the rammed refractory body of the receptacle tends to slowly migrate deeper and deeper into the heated body of the receptacle. Ultimately the filling of the pores of the portion of the refractory receptacle surrounding the core and coil with this metal leaked from the core means destroys the ability of the inductor to serve its normal purpose to act as a support for insulating the core from the coil and for supporting and containing an established channel means within the receptacle of this type of furnace. At this point the furnace must be shut down and rebuilt before the melting processes can proceed.
It is the purpose of this invention to provide an improved core and coil type of furnace by building an improved channel structure into the furnace. The improved channel structure of this invention acts to inhibit the leakage of or infiltration of the molten metal into the porous rammed refractory receptacle that supports the core and coil elements. This improved form of loop structure is provided in order to greatly increase the life expectancy of a core and coil furnace by suppressing the leakage of molten metal from the channel or loop into the somewhat porous rammed refractory receptacle that surrounds and supports the loop and coil.